Among the chemical hair dyes, the most widely used ones at present are oxidation-type hair dyes that contain more than twenty kinds of chemical components, e.g., p-phenylenediamine. In order to achieve the effect of sufficient dyeing depth, p-phenylenediamine is often used beyond the limitation during preparation; and when in use, the amount of the hair dyes is also increased by 2˜3 times, and at the same time, the dyeing time is multiplied and the dyeing temperature is increased. As a result, excessive hair dyes come into contact with the skin and are then heated, which makes it easy for benzene organics to enter the body through the skin, and is unfavorable to the health of the body due to the long-term repeated effects.
Nowadays, people pursue health and advocate naturalness, and have an urgent desire for safe and non-toxic hair dyes that do not cause skin allergy. It has become one of the hair dye development directions to do research on and develop safe and non-toxic hair dyes. Then pure natural hair dyes came into being, the main ingredients of which are pure natural elements extracted from natural plants, minerals or animals, are harmless and non-toxic to the human body, do not generate primary irritation to hairs, and do not cause skin allergy.
The advantage of the pure natural hair dyes is that they do not damage the body, while the disadvantages thereof are that the dye uptake is relatively low, the color depth of the dyed hair is not sufficient, and a saturated color can hardly be achieved even after repetition of dyeing for several times, which prevents, to a great extent, the pure natural hair dyes from being widely used.